The present invention relates generally to Magnetic Resonance Imaging (MRI) systems, and more particularly, to a method and system for improving image quality through phase correction.
Magnetic Resonance Imaging (MRI) is a well-known medical procedure for obtaining detailed, one, two and three-dimensional images of patients, using the methodology of nuclear magnetic resonance (NMR). MRI is well suited to the visualization of soft tissues and is primarily used for diagnosing disease pathologies and internal injuries.
Typical MRI systems include a superconducting magnet capable of generating a strong, homogenous magnetic field around a patient or portion of the patient; a radio-frequency (RF) transmitter and receiver system, including transmitter and receiver coils, also surrounding or impinging upon a portion of the patient; a magnetic gradient coil system also surrounding a portion of the patient; and a computer processing/imaging system, receiving the signals from the receiver coil and processing the signals into interpretable data, such as visual images.
The superconducting magnet is used in conjunction with a magnetic gradient coil assembly, which is temporally pulsed to generate a sequence of controlled gradients in the main magnetic field during a MRI data gathering sequence.
Fast spin echo (FSE) is one of the most widely used clinical MR imaging techniques for its ability to acquire T1, T2, or proton density weighted images in a relatively short period of time. Unfortunately, FSE is prone to ghosting artifacts.
The disadvantages associated with current MR systems have made it apparent that a new technique for phase correction is needed. The new technique should reduce ghosting in FSE images that result from loss of phase coherence. The present invention is directed to this end.
In accordance with one aspect of the present invention, a phase correction method for MR devices includes first acquiring a limited set of non-phase encoded echoes from which zeroth-order and first-order phase coefficients are derived. The reference data consist of a non-phase encoded FSE echo train that is acquired before and/or after the acquisition of the regular phase-encoded image data. The invention then includes applying a phase correction, using the zeroth-order and first-order phase coefficients, to the regular phase-encoded image data.
One advantage of the present invention is a reduction in FSE image ghosting and, consequently, an overall improvement in FSE image quality. Further, an improvement in the FSE image quality can lead to a more accurate clinical diagnosis, fewer repeat scans, and an increased patient throughput.
As the present invention serves to restore coherence along the echo train, another advantage is an increase in the maximum recommended echo train length. With the FSE imaging technique, an increase in the echo train length can translate into a proportionate decrease in imaging time. As a result, the present invention may serve to reduce the time required to produce an image.
Finally, FSE ghosting is known to be very sensitive to the location of off-isocenter field-of-views. As the present invention serves to reduce ghosting in FSE images, an additional advantage is a reduction in the sensitivity of isocenter positioning and consequently, a reduction in the patient setup time for certain MR examinations.
The present invention itself, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying FIGURES.